Density Of Neutral Oxygen Atoms Research Articles

Cleaning of Porous Aluminium Titanate by Oxygen Plasma

The removal of organic contaminants from porous Al2TiO5 during treatment in oxygen plasma was studied by optical emission spectroscopy (OES). The samples of Al2TiO5 were immersed into water emulsion of mineral oil for 3 h to get soaked. Then, they were thoroughly cleaned in ultrasound to remove oil from the surface. Samples were later exposed to RF oxygen plasma at the pressure of 75 Pa. The plasma density was about 2 × 1016 m−3, the electron temperature was about 6 eV and the density of neutral oxygen atoms was about 2 × 1021 m−3. Optical emission spectra between 200 and 1,000 nm were measured continuously during plasma treatment. The CO peak resulting from oil oxidation reached a well-pronounced maximum between 100 and 150 s of plasma treatment. The maximum in CO corresponded well with a minimum in O peaks. Concentration of oil in the samples was estimated by energy dispersion X-ray analysis. Initially the samples showed high concentration of carbon (about 38 at.%), while after plasma treatment the carbon concentration decreased below the detection limit. The cleaning efficiency was explained by diffusion of oil towards the surface where it was removed by oxidation with oxygen radicals.

Formation of functional groups on graphite during oxygen plasma treatment

Improved sample wettability was obtained by oxygen plasma functionalization of pyrolytic graphite. The samples were exposed to highly dissociated oxygen plasma with the density of 1×1016m−3, the electron temperature of about 5.5eV and the density of neutral oxygen atoms of 8×1021m−3 for 20s. The surface wettability was measured by a contact angle of water drop. The contact angle dropped from original 112° down to about 1°. The functional groups were detected by XPS analyses. The survey spectrum showed a substantial increase of oxygen concentration on the surface, while high-resolution analyses showed additional oxygen was bonded onto the graphite surface in the form of C–O polar functional group responsible for the increase of the surface energy.

Neutral oxygen atom density in the MESOX air plasma solar furnace facility

The density of neutral oxygen atoms in the MESOX set-up, one device of the PROMES-CNRS solar facilities, was determined by a fiber-optics catalytic probe (FOCP). Plasma was created in a flowing air within a quartz tube with the outer diameter of 5 cm by a 2.45 GHz microwave generator with the output power up to 1000 W. The flow of air was varied between 4 and 20 l/h. The O-atom density was found to increase monotonously with the increasing discharge power, and it decreased with the increasing flow rate. The degree of dissociation of oxygen molecules in the plasma column depended largely on the flow rate. At the air flow of 4 l/h it was about 80% but it decreased to about 20% at the flow of 20 l/h.

Influence of effective pumping speed on oxygen atom density in a plasma post-glow reactor

The density of neutral oxygen atoms in a post-glow reactor was measured with a fibre-optics catalytic probe. The source of O atoms was a microwave discharge generated in Ar–O 2 gas with different flow rates up to 3000 sccm/min. The O density was measured at different power of the microwave generator between 40 and 160 W and different effective pumping speed between 7 and 28 m 3/h. It was found to depend on the ratio between O 2 and Ar flow rates. At a constant O 2 flow of 200 sccm/min there was a broad maximum of O density between the Ar flow of 200 and 1000 sccm/min, independent of the effective pumping speed. At a constant O 2 and Ar flow rates of 200 and 1000 sccm/min, respectively, the O density was found to increase both with increasing power and increasing effective pumping speed. The results were explained with collision phenomena in ionized gases and heterogeneous recombination of O atoms on surfaces.

A Method for the Rapid Synthesis of Large Quantities of Metal Oxide Nanowires at Low Temperatures

A process for the rapid synthesis of metal oxide nanoparticles at low temperatures and methods which facilitate the fabrication of long metal oxide nanowires. The method is based on treatment of metals with oxygen plasma. Using oxygen plasma at low temperatures allows for rapid growth unlike other synthesis methods where nanomaterials take a long time to grow. Density of neutral oxygen atoms in plasma is a controlling factor for the yield of nanowires. The oxygen atom density window differs for different materials. By selecting the optimal oxygen atom density for various materials the yield can be maximized for nanowire synthesis of the metal.

Characterization of oxygen plasma with a fiber optic catalytic probe and determination of recombination coefficients

Fiber-optic catalytic probes were used to measure the neutral oxygen density in a postglow of a plasma reactor. Plasma was excited with an inductively coupled radio frequency generator with the frequency of 27.12 MHz and the power of 300 W. Plasma density was measured with a double Langmuir probe, while the density of neutral oxygen atoms was measured with four different fiber optic catalytic probes (Ni, Cu, Co, Nb), and NO titration. The measurements were performed at different pressure from 10 to 400 Pa. The density of neutral atoms was used to calculate recombination coefficients and their variations with plasma parameters. The results of neutral O-atom density and recombination coefficients were explained.

AES characterization of thin oxide films growing on Al foil during oxygen plasma treatment

AbstractThe oxidation phenomenon during exposure of an Al foil to a low‐pressure weakly ionized oxygen plasma was studied by Auger electron spectroscopy (AES). We used a high‐purity Al foil with a thickness of 10 µm. Prior to plasma experiments the samples were analysed by AES depth profiling. The surface composition slightly varied between samples but, generally, a native impurity film with a thickness of approximately 2.5 nm was found on the Al surface. The surface film consisted of Al, O and C. The chemical state of aluminium was determined from the Al (68 eV) and Al (51 eV) peaks. The samples were exposed to weakly ionized oxygen plasma for various periods up to 300 s. Plasma parameters were measured with Langmuir and optical fibre catalytic probes. The electron temperature was about 70 000 K, the density of charged particles was about 1 × 1016 m−3, and the density of neutral oxygen atoms 2.4 × 1021 m−3. The AES depth profiles of plasma exposed samples showed that even after a short exposure to oxygen plasma a thin but stoichiometric Al2O3 layer was formed. With further exposure to oxygen plasma the thickness of the oxide layers and broadening of the oxide/Al interface increased which was explained by thermal effects. Copyright © 2004 John Wiley & Sons, Ltd.

Selective plasma etching of powder coatings

The technology of selective plasma etching was applied in order to study particle distribution in powder coatings. Etching was performed in pure oxygen plasma. Plasma parameters were measured with a double Langmuir probe and a catalytic probe. At the neutral gas temperature of approximately 50 °C, the electron temperature was approximately 60 000 °C, the density of positive ions approximately 1×10 16 m −3, and the density of neutral oxygen atoms 2×10 21 m −3. In order to prevent sample overheating, plasma was applied in time intervals of 20 s. The removal of the polymer matrix was accomplished within 2–4 min. After plasma treatment, the samples were analyzed with a scanning electron microscope. All the pigment and filler particles were left intact thus enabling the determination of the original distribution of the particles in the coating.

Discharge cleaning of aluminum components

The rate of removal of a thin film of organic impurities during discharge cleaning in pure oxygen plasma was studied. Aluminum discs with a thickness of 2 mm and a diameter of 18 mm were first cleaned and then covered with a thin film of a polymer. The thickness of the film was estimated by AES depth profiling and was found to be about 36 nm. The samples were exposed to oxygen plasma. The plasma density and the electron temperature were measured with a double Langmuir probe and were about 1×10 16 m −3 and 6 eV, respectively. The density of neutral oxygen atoms was measured with a catalytic probe and was 3.2×10 21 m −3. Samples were exposed to the oxygen plasma in 5 s pulses in order to prevent their heating. The total treatment time was between 10 and 50 s. After plasma treatment the samples were analyzed with AES. The depth profiles showed that the thickness of the carbon layer on the surface linearly decreased with plasma exposure time. The slope of the line was about 0.8 nm/s. Taking into account the known flux of O atoms on the sample surface enabled an estimation of the probability for oxygen atoms to react with carbon on the surface. The calculated probability was about 1×10 −4.

Heterogeneous recombination of neutral oxygen atoms on niobium surface

The recombination coefficient for the reaction O+O→O 2 on a polycrystalline niobium surface was measured at various experimental conditions. The source of O atoms was a low pressure weakly ionized highly dissociated oxygen plasma created in a RF discharge. The electron temperature in plasma was about 5 eV and the density of positive ions between 5 and 10×10 15 m −3. The density of neutral oxygen atoms was measured in the afterglow with a nickel catalytic probe and was between 2.5 and 7×10 21 m −3. The recombination coefficient was measured at different temperature between 420 and 620 K, and was found to be a constant within the limits of the experimental error at the value of 0.09±0.018.

Increased surface roughness by oxygen plasma treatment of graphite/polymer composite

The technology of selective plasma etching was applied to increase the surface roughness of graphite/polymer composite. Etching was performed with a low pressure weakly ionised oxygen plasma created with a RF generator of the output power of 200 W and frequency of 27.12 MHz. The density of charged particles, density of neutral oxygen atoms and the electron temperature was about 1×10 16 m −3, 4×10 21 m −3, and 5 eV, respectively. The effects of plasma treatment were observed by scanning electron microscope (SEM), electron microprobe (EMPA) and Talysurf. It was found that the surface roughness was increased by approximately 15 times, from a virgin sample at the roughness of R a =0.27 μm to a very rough surface with R a =4 μm. The roughness increased with increasing plasma exposure time. The EMPA results showed that the amount of sulphur in the surface layer decreased with increasing etching time indicating that PPS polymer was the material etched preferentially.

Comparison of NO titration and fiber optics catalytic probes for determination of neutral oxygen atom concentration in plasmas and postglows

A comparative study of two different absolute methods NO titration and fiber optics catalytic probe (FOCP) for determination of neutral oxygen atom density is presented. Both methods were simultaneously applied for measurements of O density in a postglow of an Ar/O2 plasma created by a surfatron microwave generator with the frequency of 2.45 GHz an adjustable output power between 30 and 160 W. It was found that the two methods gave similar results. The advantages of FOCP were found to be as follows: it is a nondestructive method, it enables real time measuring of the O density, it does not require any toxic gas, and it is much faster than NO titration. The advantage of NO titration was found to be the ability to measure O density in a large range of dissociation of oxygen molecules.

Comparison of fiber optics and standard nickel catalytic probes for determination of neutral oxygen atoms concentration

The density of neutral oxygen atoms in a plasma postglow chamber was measured with a standard Ni catalytic probe and a fiber optical catalytic probe. A highly dissociated oxygen plasma was created in the discharge chamber with an inductively coupled rf generator with a frequency of 27.12 MHz and output power of 200 W. The measurements were performed in the postglow chamber where a movable recombinator for oxygen atoms was placed. The recombinator enabled the adjustment of O density independently of discharge parameters. The density of neutral oxygen atoms was determined at different pressures and different positions of the recombinator. The O density was between 5×1020 and 2×1021 m−3. The fiber probe expressed excellent repeatability as compared to the standard probe. As long as the temperature of the catalyst was above 100 °C both probes gave similar results. At a lower temperature of the standard probe, however, the optical fiber probe gave more reasonable results. The discrepancy was attributed to the decrease of the catalytic activity of nickel at lower temperatures.

A method of studying carbon particle distribution in paint films

The process of dispersion of pigment particles within the resinous component of the system is one of the most important parameters in the manufacture of any surface coating. Determining the degree of pigment dispersion is of fundamental importance, since it affects the optical, color strength and rheological properties of a paint system. In the present paper we describe a method of treatment of carbon black paint film which enables the determination of distribution of carbon black particles in the film. The method is based on selective etching of the paint using a low pressure weakly ionized highly dissociated oxygen plasma. At the pressure of 50 Pa, the neutral gas temperature of approximately 50°C, the electron temperature of 5 eV, the density of charged particles of 2×10 15 m −3 and the density of neutral oxygen atoms of 4.4×10 20 m −3, high selectivity of etching is obtained. At these conditions, optimal time of etching is approximately 30 s. The etching is due mainly to interaction of neutral oxygen atoms with surface carbon atoms and the probability for interaction is estimated to 0.026.

Determination of atomic oxygen density with a nickel catalytic probe

A nickel catalytic probe was used to determine the density of neutral oxygen atoms in a glass tube. The O source was a low pressure weakly ionized inductively coupled rf oxygen plasma. The recombination coefficient for polycrystalline nickel (purity 99.8 at. %) was determined experimentally by use of a nickel tube with a well activated surface, recombining almost all the atoms entering the experimental chamber. The recombination coefficient was found to be constant over the temperature range of 500–1100 K with a value of 0.27±0.04. The catalytic probe was a disk with a diameter of 2 mm and thickness of 0.2 mm made of the same material. The O density was measured along a glass tube (Schott 8250) with an inner diameter of 3.6 cm and length of 40 cm. The density depended on the pressure in the experimental chamber and was found to decrease exponentially along the glass tube. The characteristic penetration depth depended slightly on pressure and was 60±16 cm. Comparison of the experimental data with theoretical predictions allowed estimation of the recombination coefficient for O atoms on a Schott 8250 glass surface: γ=(1.9±0.5)10−4.